Post by
diabase1 on Jul 17, 2023 7:46am
Nordica 2
Airborne Geophysics
In 2000, the Ontario Geological Survey released maps for an airborne electromagnetic and magnetic survey covering the Kirkland Lake Area, which also covered the Nordica Intrusion. One of the maps was the shaded image of the 2nd vertical derivative of the total magnetic field (Map 82053).
Within RT Mineral's property, there are 3 northwest-southeast striking magnetic trends. From south to north, I'll call them Trend A, Trend B and Trend C. Each may represent their own unique multi-layered intrusive.
Trend A is the one that has the Windward PGE-Cu-Ni discovery, located near its extreme southeastern end. It exhibits a relatively strong magnetic intensity and has been faulted off 3 or 4 times along its length, which appears to end near the northwest corner of Nordica Township. I have interpreted a fault on Trend A, just west of a bush road. On the east side of this bush road is the Windward PGE-Cu-Ni discovery. It is this side where some major folding and faulting has taken place. It almost looks like Trend A is touching Trend C. There are 2 diabase dykes in this area that may have influenced, and disrupted the mafic/ultramafic intrusives.
Trend B is a much shorter magnetic trend, and not nearly as strong magnetically, as the other 2 trends. It also appears to terminate at the west end by a diabase dyke and an interpreted fault. I'm not sure if this trend exists within the area near the Windward Discovery area. According to Quaternary Map 2658, there is an outcrop on Trend B, just west of my interpreted fault zone, approximately 400m west of the bush road. This is another area to be looked at.
Trend C is the 3rd strong magnetic feature, which extends northwest into McEvay Township. I've interpreted one fault zone about the mid-point. As mentioned earlier, Trend C may continue east just to the north of the Windward discovery area. There is a slight fold, where the 2 diabase dykes are located.
At first glance, it appears that Trend A and Trend C (Map 82047) may be connected as a result of a major fold. However, the 'fold' is perhaps related to some severe faulting. Both trends tend to indicate that they are steeply dipping magnetic features. Trend B does not show up on this map.
On Map 82047, there are no electromagnetic responses over the Windward discovery area. This may be due to the mineralized units within the intrusive being either too narrow or the sulphides being too disseminated. However, about 400 metres west of the bush road, on Trend A, there was a 2 channel response picked up, with an amplitude of 168 ppm. It exhibits a conductance of 1-5 siemens. There was also a 'surficial' EM anomaly picked up on the tie line. However, the weakness of the latter could be due to the tie line being parallel or at a very oblique angle to the suspected bedrock conductor. I don't believe any follow-up work has been done on this anomaly!! The anomaly also shows up on the Decay Constant map (Map 82059). Gabbro has been mapped in this area (Map P.3421). There were no other EM responses picked up, on either Trend A, Trend B or Trend C.
In reference to the Apparent Conductance Map (Map 82018), the Nordica Intrusion displays an overall resistive background, except for the lone EM response mentioned earlier. The nature of the thin layers of mineralization within the intrusive has something to do with it, no doubt. One open area that may be of interest is located on the southwest corner of Sylvia Lake, which butts onto RT Mineral's claims 692299 and 807384 to the north. The anomaly is located on high ground and not in a swamp. According to Map P. 3421, the anomaly is located within and near the contact of the Watabeag Batholith and tholeiitic metavolcanics (OFR5290). The Watabeag Batholith rocks here have been described as being hornblende granodiorite. The anomaly could be related to an inlier, or an assimilation of another felsic intrusive rock type within the batholith.